There is a new dinosaur king in South America. This newly discovered top predator, named Joaquinraptor Casali, was a fast-moving hunter, about 23 feet (7 meters) long.
The body of a giant beast was then found in the leg bones of an ancient crocodile relative trapped in its jaw.
Lead author Lucio Ibiricu, a paleontologist at CONICET’s Patagonian Institute of Geology and Paleontology in Chubut, Argentina, and his colleagues unearthed the well-preserved fossil — including much of the skull, ribs, vertebrae and fore and hind-limbs — from the Lago Colhué Huapi Formation of South-central Chubut Province in central Patagonia, Argentina.
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J. Kasari is a type of theropod dinosaur known as the megaraptor, or “big thieves,” and lived in the final stages of the Cretaceous period about 70 to 66 million years ago.
Living in South America, Asia and Australia, the megarapter were carnivorous animals with long, skulls, strong arms and large claws.
Related: The oldest known dome-headed dinosaur discovered to protrude from a cliff in the Gobi desert in Mongolia
“Joaquinraptor has a clearer understanding of how this predatory group of dinosaurs lived and evolved,” Darla Zelenitsky, a paleontologist at the University of Calgary in Canada, told Live Science. “The fossil, considered the latest surviving megaraptran, offers insight into the final stages of evolutionary history in South America before its mass extinction.”
The findings revealed that megaraptrands (dinosaurs belonging to megaraptraklade, including megaraptors) were relatively large until the end of the Cretaceous period, and were likely to meet the apexual predator niches of the region in southern Patagonia at the time.
However, the land where Joaquinraptor roamed was very different from the cool, dry weather of Patagonia today. The sediments from the same layers as the fossil discovery reveal that they are probably warm, damp flood plains near the ocean.
Ibiricu told Live Science that the first hint of the fossil was discovered in 2019, but it takes three field seasons to fully unearth it. When they finally excavated the fossil, the researchers discovered the bones in the leg of a relative of a crocodile in the jawline of Joaquinraptor, hinting at its diet, and found it likely to be the area’s top predator.
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The researchers then analyzed the histology (microstructure) of the tibia and rib bones to resolve the age at the time the specimen died.
“We know based on histology that this is a sexually mature individual, but we could have grown a little more. We know that when we died, we were at least 19,” Ibiricu said.
Also, bone measurements revealed that the researchers estimated that the Joaquin Raptor was about 23 feet long and weighed 2,200 pounds (1,000 kilograms). The findings are explained in a paper published on Tuesday (September 23) in the journal Nature Communications.
“It’s a great discovery and one of the most interesting new dinosaur discoveries in recent memory,” Steve Brusatte, a paleontologist at the University of Edinburgh in Scotland who was not involved in the study, told Live Science. “It was these dinosaurs that Tyrannosaurus Rex were the best ruler in North America, and that at the same time they overturned the food chain in the South.”
Bursatte said the two predators were dramatically different. “The Joaquin Raptor was thin and slow and fast, and like a hedge trimmer, it had a ridiculously large arm and claw. Its arm and hand compared T. rex, Arnold Schwarzenegger vs Danny DeVito, at least in the arm category.
These differences would have meant that the two apex predators were hunting very clearly, Zelenitsky said. “More than four times the weight of the Joaquin Raptor, T. Rex was a brute force predator. There was a bone-shattering bite. However, Joaquin Raptor was quick, thin, attacked and attacked with surgical accuracy.
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